1. Field of the Invention
The present invention relates to a semiconductor device using an oxide semiconductor, a display device using the semiconductor device, and manufacturing methods thereof.
2. Description of the Related Art
Various metal oxides exist and are used for a variety of applications. Indium oxide is a well-known material and is used as a light-transmitting electrode material which is needed for a liquid crystal display or the like.
Some metal oxides have semiconductor characteristics. As metal oxides having semiconductor characteristics, for example, there are tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like, and a thin film transistor in which such a metal oxide having semiconductor characteristics is used for a channel formation region has been disclosed (Patent Documents 1 to 4 and Non-Patent Document 1).
Incidentally, not only unitary oxides but also multiple oxides are known as metal oxides. For example, InGaO3(ZnO)m (m is a natural number) which has a homologous phase is known as a multiple oxide semiconductor containing In, Ga, and Zn (Non-Patent Documents 2 to 4).
Further, it is confirmed that such an oxide semiconductor made of In—Ga—Zn-based oxide is applicable to a channel layer of a thin film transistor (also referred to as a “TFT”) (Patent Document 5 and Non-Patent Documents 5 and 6).
In a conventional case, amorphous silicon or polycrystalline silicon has been used for a thin film transistor (TFT) provided for each pixel of an active matrix liquid crystal display. However, a technique for manufacturing a thin film transistor using the above metal oxide semiconductor instead of such a silicon material has attracted attention. Examples of the techniques are disclosed in Patent Document 6 and Patent Document 7, where a thin film transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor for a metal oxide semiconductor film and is used as a switching element or the like of an image display device.